1. Field of the Invention
The present invention is in the field of telecommunications. In particular, the present invention relates to the routing of modem calls to internet access providers by the telephone system. Specifically, the present invention involves digital loop carriers which interface individual telephone lines to telephone central offices.
2. Discussion of the Related Art
The increasing demand for internet access is resulting in a corresponding increase in the utilization of public local telephone system resources. A telephone subscriber typically accesses the internet through an internet access provider. The telephone subscriber has a calling modem attached to his computer, and the calling modem places a call to the internet access provider's receiving modem through the public local telephone system, which also carries voice, facsimile, and other data transmissions. The connection from the calling modem's line to the internet access provider's receiving modem is typically accomplished via a free local telephone call that often has a statistically lengthy duration in comparison to a typical voice call.
In telephone networks, several telephone lines each having a unique telephone number are first routed to a digital loop carrier, rather than directly to the local central end office. The digital loop carrier has communication trunks to the local central end office, which provide a time multiplexed communication channels to the local central end office. The trunks between the digital loop carrier and the local central end office carry a limited number of DS0 communication channels. Each DS0 communication channel provides enough communication bandwidth to carry a single call. Because the telephone company realizes that many telephone numbers will likely be idle at any given time, there are fewer DS0s available in the trunks from the digital loop carrier to the local central end office than there are telephone numbers being served by the digital loop carrier. When a call is initiated, a DS0 is allocated to the call; at the end of the call, the allocated DS0 is freed up so that it may then be allocated to another new call.
Conventionally, when a calling modem initiates an internet session by dialing an internet access provider, a DS0 in a digital trunk from the digital loop carrier to the local central end office is allocated to the call, and the call is routed through the local central end office for the duration of the internet session. This allocation of the DS0 and allocation of the local central end office switch resources occupies the capacity of the local central end office for the duration of the internet session, thereby limiting the ability of the local central end office to service other calls. The congestion caused by internet calls degrades the performance of the public local telephone systems. As is apparent from the foregoing discussion, it would be desirable for the telephone company to free up as much of the existing public local telephone system's resources as possible while still providing internet access.